My LBS has a F5 Enduro on sale, and I am tempted.
If I rebuild the rear wheel, is the F5 a good choice for commuting 25-50 km a day (both ways) ?
Or I am going to destroy it at 6'2 and 375# ?

http://www.ransbikes.com/07%20F5%20Enduro/8FEnduro.jpg

http://www.ransbikes.com/F5Enduro07.htm

I suspect the frame could take it; but rather than ask us, it would be better to send RANS an email and ask them. Some of the other parts might require beefing up, too, like for instance the sprint braces or the seat base?

The "sprint braces" are the vertical rods going from the seat to the near end of the frame,right ?
About the seat base, if I disintegrate it, I'm sure i could find a solution.

You'll need to build up both wheels extra strong as the SWB puts a lot of weight on the front and with a disc brake the front wheel is dished.

No idea if the frame and such will be okay. I'd second the recommendation to call Rans and see what they suggest.